Socratic dialogues : Euthyphro, Apology, Protagoras
- Primarily moral issues are treated.
- Nascent version of the doctrine of forms is presupposed, not argued for.
- Use of the elenchus dominates dramatic development.
- “What is it?” (Ti esti?) question and Socratic definitions of central interest.
- Aporia/Socratic ignorance is typical.
- “In word and in deed”: Soc. offers a “two-tiered” defense in the Apol.
- Unity of virtues and impossibility of akrasia argued for in the Protag.
Middle period : Phaedo, Republic, Parmenides
- Metaphysics & epistemology figure more centrally.
- Elenchus drops out; Socrates is much more forthcoming, offering numerous moral definitions in the Rep.
- Doctrine of forms is developed more fully and explicitly argued for; “two-worlds” view distinguishes Being and Becoming (Parmenidean vs. Heraclitean).
- Socrates claims at Phaed. 96a-d to have no interest in natural science (the study of Becoming).
- Problems with the doctrine of forms (esp. the nature of participation and the separation of Being and Becoming) raised in the Parm.
Late dialogues : Timaeus, Theaetetus, Philebus
- Socrates virtually disappears.
- Doctrine of forms is retained, but revised and put to new uses.
- New item added to Plato’s ontology: the receptacle.
- Demiurge (divine craftsman) interposed between forms and phenomena as a causal/intentional agent.
- Participation is cashed out partly in terms of intentional relations.
- The world-soul (and human souls) are construed as mixtures of indivisible Being and divisible being; thus, the two realms are not entirely separate.
- Forms are portrayed as paradigms for, rather than exemplars of, their instances.
- New cosmology is thoroughly Pythagorean; a rigorous chemical theory is developed.
- Natural science is now a respectable discipline (contra Phaed. 96a-d), since the cosmos is a fine, divinely-created image of the form of Living Being.
- The creative activities of the demiurge are exploited for a moral purpose: our goal as humans is to become as god-like as possible, imposing order on the naturally disordered movements of our soul.
The Doctrine of Forms
Intended as a multi-purpose philosophical tool, providing the basis of several types of theory.
- Moral: forms are the standard against which human action and character are to be judged. (Euthy., Apol., Protag., Rep., Theaet., Phileb.)
- Psychological: (dim) recollection of forms permits humans to experience the perceptible realm in a relatively coherent and stable way. (Phaed.)
- Ontological: forms are the source of being, the models after which perceptible objects are fashioned. (Phaed., Rep., Tim.)
- Epistemic: forms are the objects of knowledge. (Phaed., Rep., Theaet., Phileb.)
- Semantic: (dim) recollection of forms is required for the meaningful use of ordinary predicates and facilitates successful communication. (Phaed., Rep., Parm.)
- Cosmological: forms are the models after which the entire cosmos was created. (Tim.)